AKRAMANUJAN.ORG5thNOVEMBER 2019

FUNCTION 4(15)

ramanujan1933@gmail.com

NOTE:- i am once again repeating the request for questions from other centres so that it helps you all in preparing for the orals. you can send hand written scanned sheets of questions to my e-mail given at the head. Please treat this as urgent.

(51)Main S/W line cracked during sailing.. As a second engineer how will you fabricate new pipe line.Answer:- In order not to delay the ship’s sailing, iwill carry out a temporary repair by bandaging with fibre cloth and cardobond or similar patented repair kit. To make a permanent repair at the arrival port, I will send a repair specification for workshop assistance with the pipe material specification . since it is sea water service class C galvanised steel pipe will do. I will specify the length number of flanges their details of pitch circle , no of holes and their thickness etc. I will also specify the number of bends required. If all this material is kept ready on arrival, the permanent repair can be completed during the ship’s stay in port.

(52)Describe the chemical reactions taking place during hot corrosion.Answer:- Hot corrosion is continuously occurring in exhaust valve passages where the products of combustion after their chemical reaction deposit as the gas cools, on the walls of the valve

passages. The residual fuel used in main engines in todays standards have a maximum sulphur content of 3.5 percent M/M. During combustion this sulphur combines with the oxygen from the air for combustion to form sulphur di oxide and is represented by the following equation S + O2 = SO2 --------------(1) Simultaneously the hydrogen in the fuel is combining with oxygwen from the air for combustion to form water vapour and is given by the following equation. H2+2O2 = 2H2O------------(2) The water vapour cools down to its dew point to combine with the sulphur di oxide to form a weak acid named sulphurous acid and is given by the equation SO2+H2O= H2SO3---------------------(3) This is how hot corrosion occurs.(53)What are the various checks and measurements taken in Exhaust valves after their overhaul.. What is the cooling arrangement for the valve seat.Answer:- Repeat question . refer to questionnumber (29). The valve seat is provided with a cooling water jacket through which the the cooling water is circulated.

(54)Name the various boiler water tests. How is the conductivity test for boiler water carried out.

Answer:- The regular tests that are carried out on boiler water are:

TDS or total dissolved salts , it is to find the density of the water with the dissolved salts in it.

Hardness test—it tells us to what extent the phosphates have converted the hardness salts to equivalent salts of sodim. The hardness should be below 5ppm.

Alkalinitytests consisting of caustic alkalinity and total alkalinity. Alkalinity is a desired quality in boiler water but must be within moderate limits

and hence the monitoring to check it is within limits.

Chloride test--- this test is carried out to find out if sea water is leaking into the boiler .

Phosphate reserve test--- phosphates have to be in reserve in the boiler water as the extra feed is continuously entering the boilr and has to be treated. The quantity of phosphates used should be moderate and hence the need for the test.

For boilers working on a closed feed system sulphite reserve test is carried out. Sodium sulphite is used for treating oxygen entering the system by being dissolved in the feed.

The conductivity test is the TDS carried out using an electrical probe which is dipped in the sample jar as soon as it is taken out from the boiler, the instrument is calibrated in density converted to PPM and the reading is directly read as density in PPM.

MUMBAI CENTRE FUNCTION 4April 2016 Mr Pakrasi(55)What is fuel pump lead? How do you measure it ? describe the procedure for measuring the lead and draw the sketch of the measuring tool.Answer:-The lead is the measure of the lift of the plunger in relation to barrel with the particular engine piston at TDC. The measurement is taken by placing the legs of a measuring instrument on the adjustment nut and the central pin on the plunger. The instrument used is a Vernier gauge used as a depth gauge as sketched under.

(56) What is crank shaft deflection? How do you measure it ? What do you infer fom the readings. ? how do you draw the deflection curve and what do you infer from it.Answer:- When uneven wear takes place along a line of main bearings , the effect is to cause changes in the deflections measured between the crank webs. Any change in deflection from the natural deflection can then be related to misalignment in the main bearings, as the change of deflection is proportional to the difference in height of the main bearings . Deflections are taken by placing a dial gauge into a pop marked position between the two crank webs of a crank shaft throw. The engine is turned to just after bottom dead centre, and the gauge is adjusted to zero position.

The engine is then turned and gauge reading taken when the engine is 90o before TDC, TDC, 90o after TDC and then lastly just before BDC. The two readings taken either side of BDC are averaged to give the reading at BDC.

It is normal practice to turn the engine to just after the gauge position and then reverse the turning gear to negate the lifting effect of the

turning gear. It is important that the crankshaft journals are sitting on the bottom bearing shells when taking the readings. This can be checked using feeler gauges.

Interpretation of Readings:-

1. The vertical deflection is obtained by the difference of the BDC (1) reading and (A/2 + E/2). This vertical deflection should be within the values recommended by the engine builders. If this value is high then, one of the bearings one either side of this crank has worn down and both should be examined by dismantling the

bearing keeps and measuring the wear down using a bridge gauge. The defective bearing bottom half should be renewed.

 

Plotting the Deflection Curve: A majority of the people find that the graphical representation of data is more appealing and easily understood, rather than a list of numbers hence we will see how we can use the above data to plot the deflection curve. Take a look atthe deflection curve diagram first so that you can correlate to what you read next. As you can see above on the top is the crankshaft which shows the 7units and the vertical misalignments written on top of each unit (these values are taken from the last row of the table above)A straight line is drawn beneath the crankshaft and the centre linesfrom each unit are drawn downwards through this line. This now acts as our basic centreline upon which to start plotting the deflection cur Since the first deflection is -5.2 units (remember they are normally mm unless otherwise specified), we plot this distance downwards from the reference line on

the centre line of unit 2 (not unit 1) and make the line ab which is at an angle proportional to the deflection at a. This line is further extended to intersect the centre line of the next unit.The next step is to measure the deflection from this point of intersection (downwards for negative value and upwards for positive value) and join the point from the previous point, in this case which gives rise to the line bc.This step is repeated till the last unit A smooth curve is drawn between these points and the position of this curve with respect to the base line XY gives an idea about the state of various bearings.

(57) What is a thrust block. Where is its location and give reasons for its location. What is the shape of the pad , why is it white metal lined and how does it work.Answer:- The thrust block is a device on the propulsion shafting system to transmit the propeller thrust to the hull of the ship so that the ship can move Ahead or Astern as required

The location of the thrust block and especially the thrust collar is very close to the axial node position of the axial vibrating shaft system with the engine running masses , and the propeller with entrapped water. In modern motor ships the thrust block is integral with the bedplate and positioned just after the last main bearing. The advantage of this method is that the thrust transmission atrea is made bigger and stronger, advantage of forced lubrication is made available from the engine lubrication system and the node position is also in close proximity. The node position is important because the thrust transmitted remains constant since there is no movement at the node. when vibration is occurring especially when the passage is rough. The shape of the pad is kidney shaped and the bearing face is white metal lined. (58) What is TIG,MIG welding, Brazing , and soldering.

Answer:- MIG weld welding requires three things, electricity to produce heat, an electrode to fill the joint, and shielding gas to protect the weld from the air. MIG welding is done using a very small electrode that is fed continuously, while the operator controls the amount of weld being done. In some cases when a robot takes over this process, it becomes automatic welding.

MIG Voltage Type and Welding Polarity

MIG welding unlike most other welding processes has one standard voltage type and polarity type. The voltage used is D/C direct current, much like the current in a car battery. Direct current flows in one direction, from the negative (-) to the positive (+).

The polarity used is also standard and that is D/C electrode (+) positive. This means that the handle is the positive side of the circuit, or it may be said, the electricity flows from the metal in to the welding handle.

The power source used for MIG welding is called a “constant voltage power supply”. In MIG welding the voltage is what is controlled and adjusted. When comparing MIG welding to Arc or TIG welding, MIG

welding machines use voltage settings to set the machine. TIG and Arc welding machines use amperage to set the machine or a “constant amperage power supply”.

Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode is protected from oxidation or other atmospheric contamination by an inert shielding gas (argon or helium), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing processes such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds. However, GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.[1]

Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal.Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering. The filler metal flows into the gap between close-fitting parts by capillary action. The filler metal is brought slightly above its melting (liquidus)

temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled to join the work pieces together.[1] It is similar to soldering, except for the use of higher temperatures. A major advantage of brazing is the ability to join the same or different metals with considerable strength.Soldering (AmE: /ˈsɒdərɪŋ/, BrE: /ˈsɒldərɪŋ/), is a process in which two or more items (usually metal) are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Soldering differs from welding in that soldering does not involve melting the work pieces. In brazing, the filler metal melts at a higher temperature, but the work piece metal does not melt. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated use of lead-free alloysfor electronics and plumbing purposes.59) Sketch and describe the stern tube sealing arrangement at the aft end. Describe any new type of stern bearing.Answer:- The simplex seal stern tube sealing arrangement uses lip seals made of Neoprene rubber and tightened by a garter spring so that the rubber seal rubs tightly on a chromium steel liner which is fixed to the propeller boss and turns at the speed of the propeller. The seals are fixed by holding bolts ( six in number within the seal box. The oil within the stern tube and connected to a header tank placed at a high level provides a static head of oil pressure which lubricates the white metal lined bushes within the stern tube. The high pressure lubrication aids in reducing the friction and also in transmitting the heat of friction to the water within the lower stern tube tank . This results in saving of shaft power which would otherwise be lost in friction, and also in preventing ingress of sea water into the stern tube since the oil head is higher than the head by sea water.

(60) Describe the reversing arrangement of the main engine with a suitable sketch.

Answer:-

(b)When the control is operated remote from the local emergency control station say either the Bridge or Engine control room, the reversing interlock which is activated when engine starts to turn can only be unlocked when engine stops. In this condition the reversing lever can be moved to the desired direction. This protective device is provided to safeguard the camshaft and the cams mounted on the camshaft. This also provides safety to the engine components if reversal is accomplished whilst turning has not stopped . In extreme cases it can cause slippage of journal web shrink fit.

(